Forum for Science, Industry and Business

Seismic research without artificial source

22.12.2004

Researchers at TU Delft have made progress in the theoretical foundation of a special subsoil imaging technique. This technique could be used to chart underground mineral resources, it is called “acoustic daylight imaging”. The method uses natural acoustic signals, already present in the earth, to create an image of the subsurface layers. This week, Professor Kees Wapenaar will publish an article in the renowned scientific magazine “Physical Review Letters”.

Usually, the composition of the subsurface is researched using generated acoustic signals that are sent into he ground. The sonic reflections are then analysed (the basic principle of seismics). This is no longer necessary with acoustic daylight imaging. Theoretically, taking surface measurements and subjecting the results to a series of mathematical calculations would be enough to create an image of the subsurface.

The theoretical possibility of seismic imaging using only naturally occurring sources of sound has previously been shown. This phenomenon is, however, no longer of purely theoretical importance. A current example of the possible application and development of acoustic daylight imaging is the Lofar-project in Exloo (in the Dutch province of Drente). This large scale scientific project not only encompasses the construction of the world’s largest radio-telescope, but also the realisation of the largest sensor network in Europe. This network would provide a development platform for, for example, geophysical applications.

In October of 2004, geophysicists from TU Delft, TNO and the KNMI therefore started placing geophones (a sort of microphones used to measure underground sound waves) in the testing field in Exloo. During ten years they will use these geophones to ‘listen’ to naturally occurring underground sounds. The expectation is that this will provide more understanding about the structure of the subsurface as well as providing a more accurate scientific model of how the subsurface is moving. The latter is of importance in the mining of resources such as gas, oil and coal.

Cellulose obtained from wood has amazing material properties. Empa researchers are now equipping the biodegradable material with additional functionalities to produce implants for cartilage diseases using 3D printing.

It all starts with an ear. Empa researcher Michael Hausmann removes the object shaped like a human ear from the 3D printer and explains:

The phenomenon of so-called superlubricity is known, but so far the explanation at the atomic level has been missing: for example, how does extremely low friction occur in bearings? Researchers from the Fraunhofer Institutes IWM and IWS jointly deciphered a universal mechanism of superlubricity for certain diamond-like carbon layers in combination with organic lubricants. Based on this knowledge, it is now possible to formulate design rules for supra lubricating layer-lubricant combinations. The results are presented in an article in Nature Communications, volume 10.

One of the most important prerequisites for sustainable and environmentally friendly mobility is minimizing friction. Research and industry have been dedicated...